Keynote Systems, which measures Internet performance, said that by late morning the Web sites it tracks were taking slightly longer to reach--more than 4 seconds, instead of the average 3.5 seconds.

The Web sites of the airlines whose planes were hijacked were also swarmed with traffic. American Airlines' Web site was slow Tuesday morning. Two American Airlines flights crashed: A Boeing 767 en route from Boston to Los Angeles crashed into the World Trade Center, and a Boeing 757 en route from Dulles Airport near Washington, D.C., to Los Angeles crashed at the Pentagon.

United Airlines posted a message on its site that said the airline was cooperating with the Federal Bureau of Investigation. Two United planes crashed Tuesday: A Boeing 757 crashed southeast of Pittsburgh while en route from Newark, N.J., to San Francisco. Another plane, en route from Boston to Los Angeles, also crashed. The message also included an information number for the families of the victims, 1-800-932-8555.

Internet users have set up chat groups to exchange information about the disaster. One Web site has set up an MP3 radio stream dedicated to news of the bombings, and CNN video footage can be seen at this site.

Breaking news
Several news sites were slowed or inaccessible as demand soared for information about Tuesday's attacks. All times EST.

NYTimes.com
9 a.m. 0% availability
10-11 a.m. 43% availability

ABCNews.com
9 a.m. 0% availability
11 a.m. 5% availability

USAToday.com
9 a.m. 18% availability (took 47 seconds to connect)

MSNBC.com
9 a.m. 22% availability (38 seconds to connect)

CNN.com
9-10 a.m. 0% availability

Source: Keynote

The Red Cross site was accessible Tuesday and is calling for blood donors in the New York area. The humanitarian organization said trained disaster workers from the American Red Cross of Greater New York and the National Capitol Chapter in Washington, D.C., were "providing relief in the affected areas."

Other sites temporarily flooded with requests for information were the FBI Web site, as well as the Web site for the Pentagon, which also came under attack Tuesday morning.

For more information on the attacks, refer to these links. Readers should be aware that information on these sites may not be the most credible as the situation continues to unfold.

NATIONAL SITES Remarks from President Bush on the attacks, on the White House Web site.

 The Federal Emergency Management Agency offers general information on terrorism and how the nation responds; a statement posted on the site says the agency is working with the White House and other federal agencies to assist victims of the attacks.

 The State Department's Office of Overseas Citizens Services will be closed as a result of the attacks; Americans overseas in need of emergency assistance should contact their local embassy or consulate.

United Airlines home page, with a letter from United Airlines Chief Executive Jim Goodwin.

Greyhound Lines, the country's largest intercity bus line, cancels operations in the Northeastern United States and shuts down terminals within a mile radius of any federal building, according to its Web site.

LOCAL SITESInformation about what government offices and business are closed as a result of the attacks in Washington, D.C., from the The Washington Post.

Information from The Associated Press on the status of businesses and public transportation in New York City.

Information from the city of New York's Web site. Officials are asking citizens to avoid lower Manhattan, south of Canal Street. Updates on public transportation and schools are also available.

A personal site asks New York City residents to list their names if they are "alive."

Information from the SF Gate Web site for San Francisco and the Bay Area. City Hall is evacuated; schools are closed.

Staff writers Troy Wolverton, John Borland and Aimee Male and The Associated Press contributed to this report.